CONTENTS

Page

1.0 Introduction	1

2.0 Method	2
2.1 Microbiological contamination	2
2.2 Chemical content	3
2.3 Cuticle damage	3
2.4 Keeping quality during storage	3
2.5 Water wash samples	3
2.6 Machine swabs	3

3.0 Results	4
3.1 Microbiological contamination	5
3.2 Chemical content	6
3.3 Cuticle damage	6
3.4 Keeping quality during storage	7
3.5 Wash water samples	9
3.6 Machine swabs	10

4.0 Conclusions	12

Appendices

Appendix 1 External Quality of Control and Trial Eggs from each Flock
Appendix 2 Appearance of Control and Trial Eggs under Ultra Violet Light
Appendix 3 Appearance of Control and Trial Eggs after staining with MST Cuticle Blue dye

1 INTRODUCTION

EU Egg Marketing Regulations currently prohibit the washing of Class A eggs. In many other countries with an advanced egg industry, washing is accepted as normal practice and subject to little more than official guidelines.

Egg cleaning of some kind takes place in most countries in Europe. Sweden, which recently joined the EU continues to wash many eggs. This is permitted if the eggs are graded as Class B. The free range system is naturally prone to the production of dirty eggs. Due to financial pressures, there is a temptation to wash eggs which will subsequently be marketed as Class A. MAFF Egg Marketing Inspectors publish the results of eggs downgraded due to egg washing.

At present, when washing takes place, it is normally on the production site and undertaken on a small scale with minimal control over time, temperature and chemical usage. The use of damp swabs to clean eggs is still quite common. Where small scale and traditional machines are used, eggs are often submerged. Such uncontrolled wetting can compromise the microbiological quality of eggs and is rightly discouraged.

There is evidence that modern machines which do not submerge eggs and in which the environmental conditions are carefully controlled and monitored can wash eggs satisfactorily and that past problems can be overcome.

Suggestions that egg washing would result in a decline in husbandry standards resulting in the production of more dirty eggs and that only large organisations could afford to buy the necessary equipment can now largely be discounted. Rather than debating the failings of the past, egg washing could be seen as a positive marketing tool for the future, capable of improving the appearance of the egg and reducing the risk of contamination.

This report describes the results of a trial carried out using a modern in-line egg washer/sanitiser installed at a commercial egg production site in the UK.

2 METHOD

The work was undertaken on a commercial egg production premises in the UK. The MST Gladiator 6 machine was installed in-line with eggs conveyed from cage laying houses and through the machine prior to farm packing.

The machine was thoroughly cleaned before the work began. The tests were carried out with the machine operating at its normal throughput of approximately 80 cases of eggs per hour. Eggs were tested from three different laying flocks (numbers 1, 2 and 4), which were housed in adjacent buildings. These flocks varied in age and gave a progression from young (average age of 25 weeks) to middle aged (45 weeks of age) and finally end of lay birds (66 weeks of age).

All the testing was undertaken in a single operation over a period of approximately 4 hours. A standard chemical treatment was used as per the manufacturer’s specifications.

Samples of both sanitised (trial) and non-sanitised (control) eggs were collected from each of the three flocks using appropriate protocols. The eggs were transported to the ADAS Laboratories at Wolverhampton where they were analysed for microbiological contamination, chemical content, cuticle damage and keeping quality during storage.

Samples of wash water and swabs from the machine itself were also collected on site for analysis.

Each of these analyses is described in more detail below.

2.1 Microbiological Contamination

Samples of test and control eggs from each of the three flocks were carefully collected by hand (protected with polythene gloves). The test eggs were collected after sanitising and drying, the control eggs were taken from the conveyor rollers immediately before they entered the MST machine section. There were therefore six different samples in total.

The eggs were packed onto new keyes trays and placed inside polythene bags which were immediately sealed.

Microbiological assessments were made on 12 eggs from each of the six samples. Assessments were made for both total viable bacteria count (TVC) and enterobacteriaceae. Three separate tests were undertaken to assess TVC and enterobacteriaceae as follows :-

on the surface of the shell

within the shell and the shell membranes

within the liquid contents of the egg.

2.2 Chemical Content

Repeat samples of eggs were collected from each treatment as described in Section 2.1 above. The contents of both sanitised and control eggs from each of the three different flocks were analysed for pH, and the content of iron, chloride and calcium.

2.3 Cuticle Damage

The quality of the cuticle in both sanitised and control eggs from each flock was viewed on site using ultra-violet light. Samples of eggs were also taken back to the Laboratory where they were immersed in a dye solution (MST Cuticle Blue). A record was kept by taking pictures of each test using a digital camera.

2.4 Keeping Quality During Storage

A total of 150 eggs from each of the three flocks were collected both before and after sanitisation. These were transported to the Laboratory and held in controlled temperature conditions at approximately 15°C. The effect of sanitisation on the physical quality of eggs during storage was assessed by measuring albumen quality in Haugh Units during a 28 day storage period.

After 1, 8, 15, 22 and 28 days of storage, assessments were made, using samples of 30 eggs for each test . At day 1, eggs were also measured for shell density to give an indication of the quality of the shells produced by each flock.

2.5 Wash Water Samples

Both microbiological and chemical assessments were made of the water used for sanitisation. A sample of water was collected from source as the machine was being filled. Further samples were collected from each of the three water tanks on the machine after it had operated for 30 minutes, 2 hours and 4 hours.

Each sample of water was analysed for total viable bacterial count (TVC) and enterobacteriaceae by plate count and also for pH, calcium, chloride and iron.

2.6 Machine Swabs

Swabs were taken from the machine at the start of the run and again approximately 4 hours later. Swabs were taken from the dry rollers on the conveyor in front of the machine, from the rollers within the machine and finally from the rollers in the drier section of the machine.

As before, these were tested for total viable count and enterobacteriaceae.

3 RESULTS

The overall appearance of the ungraded eggs was broadly as expected for young, medium and old flocks. The shell density was measured using 60 eggs from each flock (30 control and 30 trial eggs). The mean results are summarised in Table 1.

Table 1 - Mean Shell Density (mg/cm²) of Eggs in each Flock

(Sample Size 30 eggs)

Flock Age (weeks)	Control	Trial
25	83.0	81.0
45	77.0	80.0
66	79.0	80.0

Figure 1 shows that results for the young and old flocks are within current ADAS Targets. The 45 week old flock failed to reach the target band.

Levels of visibly soiled eggs prior to sanitising appeared approximately in line with normal commercial standards. After sanitising, the eggs were uniformly physically clean and there were no visible signs of damage. Pictures of 30 eggs from each flock, both control and trial are shown in Appendix 1 at the back of this report.

It was noted that the water temperatures in the machine were lower than those advised by MS Technologies. The range was from around 33°C in the first (pre-wash) tank to just over 40°C in the third (rinse).

3.1 Microbiological Contamination

The results of microbiological tests on outer shells, inner shells/membranes and egg contents are presented in Table 2 (Total Viable Count) and Table 3 (Enterobacteriaeceae) below.

Table 2 shows that TVC levels were consistently lower on the outer shell after sanitising. It appeared that levels in the inner shell and the shell membranes also tended to be lower. Levels in the egg contents were very low both in the control and the test eggs. Table 3 shows that enterobacteriaceae levels were generally low both in control and test eggs.

Table 2 - Total Viable Count at 30^oC (CFU/g) in Control and Test Eggs

	CONTROL	TEST
Outer shell (25 week old flock)	55,000	9
Outer shell (45 week old flock)	28,000	130
Outer shell (66 week old flock)	65,000	13

Inner shell/membrane (25)	850	350
Inner shell/membrane (45)	600	600
Inner shell/membrane (66)	3,200	40

Egg contents (25)	40	40
Egg contents (45)	40	30
Egg contents (66)	50	3

Table 3 - Enterobacteriaceae at 37^oC (CFU/g) in Control and Test Eggs

	CONTROL	TEST

Outer shell (25)	9	<1
Outer shell (45)	<1	<1
Outer shell (66)	<1	<1

Inner shell/membrane (25)	<10	<10
Inner shell/membrane (45)	<10	150
Inner shell/membrane (66)	1100	<10

Egg contents (25)	<1	<1
Egg contents (45	<1	<1
Egg contents (66)	1	<1

3.2 Chemical Content

The results of chemical tests on egg contents are presented in Table 4 below.

Table 4 - Chemical Analysis of Control and Test Eggs

	CONTROL	TEST
pH(25)	7.8	7.8
pH(45)	7.7	7.8
pH(66)	7.6	7.5

Iron(25)	15.0mg/kg	13.6mg/kg
Iron(45)	14.3	16.0
Iron(66)	16.0	14.6

Chloride (25)	1320mg/kg	583mg/kg
Chloride (45)	1310	1150
Chloride (66)	428	692

Calcium (25)	429mg/kg	480mg/kg
Calcium (45)	450	464
Calcium (66)	526	521

The pH and contents of iron and calcium were very similar in both control and test egg contents irrespective of flock age. The results of the analyses of chloride showed far greater variation but no consistent trend.

3.3 Cuticle Damage

A pictorial summary of the appearance of the eggs both under ultra violet light and following cuticle stain is given in Appendices 2 and 3 at the end of the report.

3.4 Keeping Quality During Storage

The results of the albumen quality assessments are shown in Table 5 below and summarised in 3 graphs shown in Figures 2, 3 and 4. There did not appear to be a clear difference between the control and test eggs in terms of their physical appearance after storage.

Table 5 - Albumen Quality (Haugh Units) of Control and

Test Eggs During Storage

	CONTROL	TEST

Age of eggs - 1 day
Flock 1 (25)	91	90
Flock 2 (45)	88	83
Flock 4 (66)	75	76

Age of eggs - 8 days
Flock 1 (25)	80	75
Flock 2 (45)	70	65
Flock 4 (66)	64	61

Age of eggs - 15 days
Flock 1 (25)	72	80
Flock 2 (45)	67	64
Flock 4 (66)	59	53

Age of eggs - 22 days
Flock 1 (25)	69	73
Flock 2 (45)	67	67
Flock 4 (66)	60	63

Age of eggs - 28 days
Flock 1 (25)	68	66
Flock 2 (45)	59	60
Flock 4 (66)	53	55

Click following for ‘PDF’ photographs

Control eggs (5,014 KB)

Ultra Violet inspection (4,810KB)

Cuticle Blue Analysis (5,022KB)

3.5 Wash Water Samples

The results of the microbiological and chemical tests are shown in Tables 6 and 7 below.

Table 6 - Microbiological Tests

Total Viable Count at 30⁰C (CFU/ml) and Enterobacteriaceae

at 37⁰C (CFU/ml) in Machine Tank Water

	TVC (CFU/ml)	ENTEROBACTERIACEAE (CFU/ml)
Water from Source	11	<1
After 30 mins
Tank 1	6	<1
Tank 2	54	<1
Tank 3	390	2

After 2 hours
Tank 1	800	<1
Tank 3	6500	14

After 4 hours
Tank 1	1300	<1
Tank 2	41	<1
Tank 3	150	<1

The microbiological results show increasing TVC levels from 30 minutes to 2 hours and as expected, higher counts in Tank 3 than in Tank 1. After four hours, the levels were generally lower and the trend was reversed.

Levels of enterobacteriaceae were very low in all samples.

Table 7 - Chemical Tests

Chemical Analysis of Machine Tank Water

	pH	IRON (mg/kg)	CHLORIDE (mg/kg)	CALCIUM (mg/kg)

Water from source	7.1	<0.10	112	58.2

After 30 mins.
Tank 1	7.0	<0.10	455	67.5
Tank 2	6.9	<0.10	471	68.7
Tank 3	6.9	<0.10	454	68.2

After 2 hours
Tank 1	7.2	0.13	491	93.6
Tank 3	7.2	0.14	493	92.8

After 4 hours
Tank 1	7.4	0.15	507	96.5
Tank 2	7.3	0.14	539	97.6
Tank 3	7.3	0.17	496	97.4

The results show that at any one time the pH and the contents of iron, chloride and calcium were similar in the three water tanks but with time, the pH increased slowly and the levels of iron, chloride and calcium were also higher. After 4 hours the maximum iron content (in Tank 3) was 0.17 mg/kg.

3.6 Machine Swabs

The results of the microbiological testing of machine swabs are shown in Table 8 below. TVC levels were highest on the dry rollers before the machine. Enterobacteriaceae levels were very low in all samples.

Table 8

Total Viable Count at 30⁰C (CFU/ML) and

Enterobacteriaceae at 37⁰C (CFU/ml) in Swab Tests

	TVC (CFU/ml)	ENTEROBACTERIACEAE (CFU/ml)

At start of Run
Dry rollers	480,000	<10
Rollers in machine	30	<10
Rollers in dryer	2,000	<10

After 4 hours
Dry rollers	560,000	<10
Rollers in machine	3,200	<10
Rollers in dryer	940	<10

4 CONCLUSIONS

All eggs were effectively washed so that visible contamination was removed. There was no indication that eggs were physically damaged during the process.

Bacterial levels on the shell surface were much lower on the sanitised eggs than the controls. The total viable count appeared slightly higher in the inner shell and membranes of the control eggs, even though the storage time prior to testing was minimal.

The pH and the contents of iron and calcium were consistent and similar in both control and test eggs. The chloride levels showed much more variation in both sets of eggs.

The keeping quality of the eggs, as assessed by the physical appearance of the albumen appeared to be similar both in control and test eggs.

The wash water samples showed expected differences in microbiological quality between the prewash and the rinse tank after 30 minutes and 2 hours with bacterial levels increasing with time. The results after 4 hours are not consistent with the other results.

The chemical analyses of the machine tank water were very consistent. A gradual (although small) increase with time was seen in the pH of the water and in the contents of iron, chloride and calcium.

ADAS Gleadthorpe

Meden Vale